Hydraulic actuator with mechanical piston position feedback

Abstract

A hydraulic actuator for a downhole pump system includes a piston housing having a head end and a base end. A drive piston is movable within the piston housing between a first piston position proximate to the head end and a second piston position proximate to the base end. The hydraulic actuator includes a control valve that translates between a first control valve position in which fluid is directed into the base end and a second control valve position in which fluid is directed into the head. When the piston moves to the first piston position, a mechanical positon feedback system translates the control valve from the first control valve position to the second control valve position. When the piston moves to the second piston position, the mechanical positon feedback system translates the control valve from the second control valve position to the first control valve position.

What is claimed is: 
     
         1 . A hydraulic actuator comprising:
 a piston housing having a head end and a base end opposite said head end;   a drive piston disposed within said piston housing and movable between a first piston position proximate to said head end and a second piston position proximate to said base end;   a control valve positionable between a first control valve position and a second control valve position, wherein:
 in the first control valve position, said control valve is configured to direct fluid into said base end; and 
 in the second control valve position, said control valve is configured to direct fluid into said head end; and 
   a mechanical position feedback system configured to:
 translate said control valve from the first control valve position to the second control valve position in response to said drive piston moving to the first piston position; and 
 translate said control valve from the second control valve position to the first control valve position in response to said drive piston moving to the second piston position. 
   
     
     
         2 . The hydraulic actuator in accordance with  claim 1 , wherein said mechanical position feedback system comprises:
 a first mini piston cylinder coupled in fluid communication with said control valve, said first mini piston cylinder configured to, when actuated, transition said control valve from the first control valve position to the second control valve position; and   a second mini piston cylinder coupled in fluid communication with said control valve, said second mini piston cylinder configured to, when actuated, transition said control valve from the second control valve position to the first control valve position.   
     
     
         3 . The hydraulic actuator in accordance with  claim 2 , wherein said mechanical position feedback system further comprises a piston rod coupled to said drive piston, said piston rod comprising an extension disposed between said first mini piston cylinder and said second mini piston cylinder, wherein said extension is configured to:
 actuate said first mini piston cylinder when said drive piston moves to the second piston position; and   actuate said second mini piston cylinder when said drive piston moves to the first piston position.   
     
     
         4 . The hydraulic actuator in accordance with  claim 2 , wherein said second mini piston cylinder is disposed in said head end, wherein said mechanical feedback system further comprises a cable coupling said drive piston to said second mini piston cylinder, said cable configured to actuate said second mini piston cylinder by pulling said second mini piston cylinder in response to said drive piston moving to the second piston position. 
     
     
         5 . The hydraulic actuator in accordance with  claim 2 , wherein each of said first mini piston cylinder and said second mini piston cylinder comprises a spring configured to decelerate said first mini piston cylinder and said second mini piston cylinder when actuated. 
     
     
         6 . The hydraulic actuator in accordance with  claim 1 , wherein said mechanical position feedback system comprises:
 a piston rod coupled to said drive piston, said piston rod comprising an extension; and   a mechanical linkage coupled to said control valve, said linkage configured to be actuated between a first linkage position and a second linkage position by said extension in response to said drive piston moving to the first piston position and the second piston position, respectively, wherein said mechanical linkage is configured to:
 translate said control valve from the first control valve position to the second control valve position in response to said mechanical linkage translating to the first linkage location; and 
 translate said control valve from the second control valve position to the first control valve position in response to said mechanical linkage translating to the second linkage position. 
   
     
     
         7 . The hydraulic actuator in accordance with  claim 6 , wherein said piston housing is disposed between said extension and said control valve, and said mechanical linkage extends proximate to said piston housing. 
     
     
         8 . The hydraulic actuator in accordance with  claim 1  further comprising at least one deceleration feature proximate to at least one of the first piston position and the second piston position. 
     
     
         9 . The hydraulic actuator in accordance with  claim 8 , wherein said at least one deceleration feature comprises at least one of a groove defined by said piston housing, a spring, a hydraulic cushion, and a bumper. 
     
     
         10 . The hydraulic actuator in accordance with  claim 1 , wherein said control valve comprises at least one of a two-position, detented, four-way directional control valve and a three-position, detented, four-way directional control valve. 
     
     
         11 . The hydraulic actuator in accordance with  claim 1  further comprising at least one of an accumulator and a compensator bag, coupled in fluid communication with said piston housing and said control valve. 
     
     
         12 . The hydraulic actuator in accordance with  claim 1  further comprising:
 an actuator motor; and 
 an actuator pump coupled to said actuator motor and coupled in fluid communication with said control valve, said actuator pump configured to provide fluid to said control valve. 
 
     
     
         13 . A downhole pump system comprising:
 a piston rod pump assembly; and   a hydraulic actuator coupled to said piston rod pump assembly, said hydraulic actuator comprising:
 a piston housing having a head end and a base end opposite said head end; 
 a drive piston disposed within said piston housing and movable between a first piston position proximate to said head end and a second piston position proximate to said base end; 
 a control valve positionable between a first control valve position and a second control valve position, wherein:
 in the first control valve position, said control valve is configured to direct fluid into said base end; and 
 in the second control valve position, said control valve is configured to direct fluid into said head end; and 
 
 a mechanical position feedback system configured to:
 translate said control valve from the first control valve position to the second control valve position in response to said drive piston moving to the first piston position; and 
 translate said control valve from the second control valve position to the first control valve position in response to said drive piston moving to the second piston position. 
 
   
     
     
         14 . The downhole pump system in accordance with  claim 13 , wherein said mechanical position feedback system comprises:
 a first mini piston cylinder coupled in fluid communication with said control valve, said first mini piston cylinder configured to, when actuated, transition said control valve from the first control valve position to the second control valve position; and   a second mini piston cylinder coupled in fluid communication with said control valve, said second mini piston cylinder configured to, when actuated, transition said control valve from the second control valve position to the first control valve position.   
     
     
         15 . The downhole pump system in accordance with  claim 14 , wherein said mechanical position feedback system further comprises a piston rod coupled to said drive piston, said piston rod comprising an extension disposed between said first mini piston cylinder and said second mini piston cylinder, wherein said extension is configured to:
 actuate said first mini piston cylinder when said drive piston moves to the second piston position; and   actuate said second mini piston cylinder when said drive piston moves to the first piston position.   
     
     
         16 . The downhole pump system in accordance with  claim 14 , wherein said second mini piston cylinder is disposed in said head end, wherein said mechanical feedback system further comprises:
 a cable coupling said drive piston to said second mini piston cylinder, said cable configured to actuate said second mini piston cylinder by pulling said second mini piston cylinder in response to said drive piston moving to the second piston position.   
     
     
         17 . The downhole pump system in accordance with  claim 14 , wherein said mechanical position feedback system comprises:
 a piston rod coupled to said drive piston, said piston rod comprising an extension; and   a mechanical linkage coupled to said control valve, said mechanical linkage configured to be actuated between a first linkage position and a second linkage position by said extension in response to said drive piston moving to the first piston position and the second piston position, respectively, wherein said mechanical linkage is configured to:
 translate said control valve from the first control valve position to the second control valve position in response to said mechanical linkage translating to the first linkage location; and 
 translate said control valve from the second control valve position to the first control valve position in response to said mechanical linkage translating to the second linkage position. 
   
     
     
         18 . A method of controlling a hydraulic actuator, the hydraulic actuator including a piston housing having a head end and a base end opposite the head end, a drive piston disposed within the piston housing and movable between a first piston position proximate to the head end and a second piston position proximate to the base end, and a control valve positionable between a first control valve position and a second control valve position, said method comprising:
 determining, using a mechanical position feedback system, that the drive piston has moved into the second piston position;   transitioning, in response to determining that the drive piston has moved into the second piston position, the control valve from the second control valve position to the first control valve position, wherein in the first control valve position, the control valve directs fluid into the base end of the piston housing;   determining, using the mechanical position feedback system, that the drive piston has moved into the first piston position; and   transitioning, in response to determining that the drive piston has moved into the first piston position, the control valve from the first control valve position to the second control valve position, wherein in the second control valve position, the control valve directs fluid into the head end of the piston housing.   
     
     
         19 . The method in accordance with  claim 18 , wherein the mechanical position feedback system includes a first mini piston cylinder coupled in fluid communication with the control valve and a second mini piston cylinder coupled in fluid communication with the control valve, said method further comprising:
 actuating the first mini piston cylinder to transition the control valve from the first control valve position to the second control valve position; and   actuating the second mini piston cylinder to transition the control valve from the second control valve position to the first control valve position.   
     
     
         20 . The method in accordance with  claim 18 , wherein the mechanical feedback system includes a mechanical linkage coupled to the control valve, said method further comprising:
 actuating the mechanical linkage to a first linkage position to translate the control valve from the first control valve position to the second control valve position; and   actuating the mechanical linkage to a second linkage position to translate the control valve from the second control valve position to the first control valve position.